1. Field of the Invention
The present invention relates to an ink-jet recording apparatus which records an image on a recording medium, and a method of preventing clogging of nozzles which discharge ink of ink-jet heads mounted on the ink-jet recording apparatus.
2. Description of the Related Art
As ink-jet recording apparatus, known is an on-demand ink-jet printer. This ink-jet printer comprises an ink-jet head having nozzles for discharging ink and ink chambers for storing ink. The ink-jet printer discharges ink from the nozzles by changing the volume of the ink chambers, and forms an image on a recording medium. As controlling methods of providing change in volume in the ink chambers, there are a piezoelectric controlling method utilizing distortion of a piezoelectric member, and a control method using a heating element. It is possible to perform on-demand printing by providing change in volume to each ink chamber by the above controlling methods. In such conventional ink-jet printers, negative pressure is always applied to the ink chambers and the nozzles, such that the ink surface (meniscus) is formed on the reverse side of the ink discharging direction. This is performed to prevent leakage of ink from the nozzles other than when necessary, such as recording, and prevent soiling a medium such as paper by discharging ink only when necessary.
However, when the ink-jet head is left for a long time in the state where negative pressure is applied to the ink chambers and the nozzles, if air bubbles or waste adhere to the nozzles, they easily enter the nozzles by the influence of vibration and the like. Further, when the ink-jet head is left for a long time, moisture and volatile components evaporate from the ink in the nozzles. In particular, it causes a local increase in viscosity in edge portion of the ink surface (meniscus), and causes condensation of color material of ink. Thereby, performing recording operation after leaving the ink-jet head for a long time causes non-discharge or discharge failure of ink.